Code review comment for lp:~andreas-pokorny/mir/rebase-fix-1550050

lp:mir is series 0.21, which is clear in the launchpad config:
https://launchpad.net/mir

So lp:mir should always call itself series 0.21 until such time as that's released and we're working on series 0.22.

If you want to release a 0.20.3 then that must occur in lp:mir/0.20.